A resistance change memory is a semiconductor memory using a variable resistance element as a recording medium. The variable resistance element is an element made of a material that changes its resistance value in accordance with, e.g., a voltage, electric current, or heat, and includes a phase change element. For example, a ReRAM (Resistance Random Access Memory) using a metal oxide as a variable resistance element is expected as a next-generation semiconductor memory having a large capacity and capable of a high-speed operation.
The capacity can be increased by, e.g., giving a three-dimensional structure to a memory cell array, or storing multi-level data in the variable resistance element. A resistance change memory adopts a cross-point type memory cell array, and hence is suited to construction of a three-dimensional structure by stacking memory cell arrays (see, e.g., patent reference 1).
Presently, however, it is difficult to give a three-dimensional structure to a peripheral circuit even when a three-dimensional memory cell array is possible. Accordingly, the number of stackable memory cell arrays is limited by the size of the formation region of drivers for driving conductive lines in these memory cell arrays. That is, the number of drivers is proportional to the number of memory cell arrays, whereas it is impossible to unlimitedly enlarge the driver formation region on a semiconductor substrate.
Also, when stacking memory cell arrays, the time constant of a via plug for connecting a conductive line in a memory cell array and a driver for driving the conductive line changes from one memory cell array to another. On the other hand, the size (channel width) of an FET (Field Effect Transistor) as a driver is constant. Therefore, based on the time constant (maximum value) of a via plug for connecting a conductive line (uppermost conductive line) in an uppermost memory cell array and a driver for driving the conductive line, the size of all drivers is set to a size enough to drive the uppermost conductive line.
From the foregoing, it is conventionally necessary to form drivers having a large uniform size in a limited region. This makes it impossible to sufficiently obtain the benefit of a large capacity of a three-dimensional memory cell array.